Immunization with HIV spike proteins elicits antibody responses directed largely against variable epitopes in the native HIV gpl20/41 trimer with little, if any broad neutralizing specificity. However, several broadly neutralizing antibodies recognize the highly conserved Membrane-Proximal External Region (MPER) of the gp41 fusion protein. To elicit antibody responses focused against this conserved fragment of gp41, we propose a strategy based on the association of MPER peptides with 'lipid-enveloped nanoparticles' (NPs), virion-sized synthetic nanoparticles with a bioresorbable polymer or aqueous core and lipid surface layer. This approach is motivated by preliminary data showing the structure of MPER peptides associated with lipid membranes, which assume a conformation recognized by the broadly neutralizing antibody (BNAb) 4E10. The core of these particles can be used to provide co-delivery of T-helper epitopes, while MPER peptides and TLR ligands are presented from the lipid particle surface. The specific aims are: (1) We will determine optimal MPER presentation for BNAb recognition in terms of particle surface lipid composition and MPER peptide anchoring. (2) We will test whether encapsulation of T helper epitopes in the core of NPs can support the generation of CD4+ T cell help for antibody responses without misdirecting the antibody response away from the particle surface-displayed MPER peptide. (3) We will analyze the impact of TLR ligand incorporation into particle surfaces, to adjuvant dendritic cell, B-cell, and helper T-cell activation and resulting antibody responses to MPER peptides, and test the ability of NPs to deliver adenosinergic signaling inhibitors as co-adjuvants. Together, these strategies will be used to generate an HIV vaccine that elicits BNAb responses, with in vivo responses in mice analyzed in collaboration with Project 1. This unique structural approach to creation of an HIV vaccine seeks to combine key structural information about conserved residues of the HIV virus with a nanoparticle-base delivery strategy to achieve a neutralizing antibody response capable of broad prophylactic protection.